Multipartite concurrence of W-class states based on sub-partite quantum systems.

We study the concurrence for arbitrary N-partite W-class states based on the (N - 1) -partite partitions of subsystems by taking account to the structures of W-class states. By using the method of permutation and combination, we give some analytical formulas of concurrence and elegant relations between the N-partite concurrence and the (N - 1) -partite concurrence for arbitrary N-partite W-class states. Applying these relations, we present better lower bounds of concurrence for some multipartite mixed states. An example is given to demonstrate that our lower bounds can detect more entanglements. [ABSTRACT FROM AUTHOR]